Which statement best defines fixture efficiency in indoor water use?

• A. The amount of water a fixture uses per use; quantified as gpf or gpm.
• B. The total annual water use of a building.
• C. The rate of water flow at the fixture.
• D. The energy required to heat water for the fixture.

Answer: (D)

Fixture efficiency in indoor water use is about how effectively a fixture delivers the desired water service while minimizing the additional resources required. The energy needed to heat that water directly ties to overall resource efficiency, so a fixture that uses less energy to heat the same amount of water is more efficient.

The other statements describe how much water is used per use, total annual water use, or the immediate flow rate, which tell you about consumption or performance but not how efficiently the fixture uses energy to provide the service. Hence, the energy required to heat water best defines fixture efficiency.